Many battery powered applications perform best at a supply voltage that differs from the battery voltage. DC-DC converters are designed to solve this problem, and many different types of converters exist for this purpose. Battery powered applications often require low quiescent current DC-DC conversion to extend battery life or optimize performance.
It is also beneficial in many battery power applications to know how many Coulombs have been consumed since the battery was installed or fully charged. This information is often the only reliable means for estimating the remaining battery life—especially in cases where the battery discharge curve is very flat (e.g., Li-SOCL2 batteries, etc.) and the battery voltage provides no useful basis for estimating state of charge.
Conventional Coulomb counters continuously monitor current flowing into or out of a battery and keep a running tally of Coulombs that have passed through the external sense resistor. In the case of a discharging battery, Coulombs consumed are calculated by multiplying the average current by the total time.
However, continuous monitoring of the battery current requires relatively high operating current which in turn discharges the battery. In a conventional Coulomb counter, the quiescent current may be between 70 μA and 100 μA which is unacceptably high for many long lifetime primary cell battery applications. Without continuous monitoring, a conventional Coulomb counter may miss significant discharge events. Also, the Coulomb counter accuracy could suffer greatly.
Therefore, there is a need for a new technique that would combine low quiescent current DC-DC conversion with low current and accurate Coulomb counting.